(1) Field of the Invention
The present invention relates to a semiconductor device, and more particularly to a semiconductor device of the vertical surface-mounting type.
(2) Description of the Related Art
Prior art semiconductor devices of vertical surface-mounting type have been developed for enhancing the mounting density per unit area of a printed circuit board when mounting a large number of parts in cases where they are not subject to particular restriction on the height of mounting on the printed circuit board. In this type of semiconductor device, surface-mounting is done with the printed circuit board held upright, and to this end the device has support leads for supporting it.
FIGS. 1A, 1B and 1C show a typical prior art semiconductor device of the type described above. As shown therein, the device comprises a die pad 11 for mounting a semiconductor die 1 thereon, hanging leads 12 for supporting the die pad 11, inner leads 3A integral with outer leads 3B, bonding wires 6 for electrically connecting the inner leads 3A and pads 4 of the semiconductor die 1, support leads 5A and 5B for supporting the body of the semiconductor device in an upright position on a printed circuit board, and a molded resin 8 for sealing these parts therein.
The outer leads 3B project in a row from the molded resin sealer 8. Each of the outer leads 3B has an end which is bent in an L-shaped form in one direction. The support leads 5A and 5B which support the body of the semiconductor device are provided in two pairs each disposed adjacent each end of the row of the outer leads 3B. In the same way as the outer leads 3B, the support leads 5A and 5B in each pair have their respective ends L-shaped in opposite directions. The support leads 5A and 5B are provided for the sole purpose of supporting the semiconductor device so that they are dummy leads not electrically connected to the semiconductor die 1. They are secured by soldering to the printed circuit board in the same as are the outer leads 3B.
In the above prior art semiconductor device of the vertical surface-mounting type, heat generated due to power consumption by the semiconductor die can escape from the die pad 11 or the semiconductor die surface only through the molded resin 8 to the outside. Thus, the obtainable heat resistance of the semiconductor device is only 70.degree..about.80.degree. C./W. Therefore, when the power consumption of the semiconductor die exceeds 0.8 W, heat can no longer sufficiently escape to the outside. It is possible to somewhat reduce the heat resistance of the semiconductor device by increasing the size of the die pad. However, since the inner leads 3A and the die pad 11 are made from the same lead frame, the size of the die pad 11 is restricted by the length of the inner leads 3A, and therefore it is difficult to increase the size of the die pad.
In a further respect, while the support leads 5A and 5B which support the semiconductor device in the vertical form are dummy leads that are not utilized electrically, it is nevertheless necessary, in the semiconductor device of the vertical surface-mounting type, to provide areas for these support leads. This imposes restrictions on the number and dimensions, i.e., size, of the outer leads 3B for signals, which is undesirable when seeking to increase the number of pins of the semiconductor device.